1. Field of the Invention
The present invention relates to image forming systems that include sheet-conveying devices, and image forming apparatuses and control methods thereof.
2. Description of the Related Art
In recent years the image quality of electrophotographic and inkjet method image forming apparatuses has begun to approach the image quality of offset printing and therefore many such image forming apparatuses are introduced even in the field of commercial printing.
On the other hand, attention is being given to on-demand printing in the field of commercial printing. On-demand printing refers to print processing that is executed based on print data sent from a customer via a telecommunications line. On-demand printing can also flexibly support demand for diversified, small quantity printing and therefore is also suited to printing of documents such as manuals and individually targeted pamphlets, for example. Furthermore, on-demand printing has many advantages such as major reductions in printed stock, major reductions in labor and time due to being able to go online from receiving data until completion of binding, and the ease of data transfers.
In regard thereof, a plurality of large capacity sheet-feeding units are connected in image forming systems used in on-demand printing in order to support a wide variety of recording materials. Furthermore, a plurality of post-process devices are necessary to achieve post-processing such as alignment, sorting, z-folding, inserter processing, stapling, punch hole opening, and bookbinding processing.
However, starting and stopping all of the plurality of sheet-feeding units and plurality of post-process devices as a group involves consuming wasted energy and increasing noise pollution, and is therefore not preferable.
Conventionally, an invention has been proposed (Japanese Patent Laid-Open No. 2005-195929) in which an individual post-process device independently stops operation when a determination is made in response to paper destination information that a predetermined number or more of sheets is not to be transported to the device.
However, some post-process devices among a plurality of post-process devices having stopped their operation may require a preparatory operation for restarting. Accordingly, there is a risk that throughput of the image forming system will be reduced undesirably when individual post-process devices stop operation by themselves. Furthermore, in the image forming system of Japanese Patent Laid-Open No. 2005-195929, each post-process device always waits for the predetermined number of sheets of paper to arrive at the device itself before stopping. Hence, throughput is reduced undesirably when there is no necessity to wait for the arrival of the predetermined number of sheets of paper. It should be noted that Japanese Patent Laid-Open No. 2005-195929 gives attention to post-process devices, but does not give attention to sheet-feeding units.